I have a Centos 5 mail server setup with postfix and dovecot (+ postfix admin). Dovecot autentification is trough mysql database (which is updated with postfix admin). Passwords are stored in md5.

Now my smtp server is closed relay, I want to open it for mailboxes/users I've created trough postfix admin. They should input the same username/password I've created with postfix admin to be able to send email trough my smtp server.